1. Field of the Invention
The present invention generally relates to data communication for purposes such as Digital Satellite Equipment Control (DiSEqC), and more particularly, to a data receiving circuit that is capable of properly receiving current modulated signals having a wide range of frequencies.
2. Background Information
Data communication for DiSEqC has historically been performed through the modulation of a 22 kHz voltage tone. This modulated tone may be superimposed onto a direct current (DC) voltage that powers one or more low noise blocks (LNBs) of a satellite receiving system. Using DiSEqC, an integrated receiver/decoder (IRD) apparatus (e.g., set-top box, etc.) may for example transmit signals via a transmission medium such as coaxial cable that enable selection and control of a particular LNB via a switching unit. DiSEqC communication may also include a return channel (e.g., on the same transmission medium) in which current modulated signals are transmitted from the LNB and/or switching unit back to the IRD apparatus.
IRD apparatuses may include dedicated circuitry for receiving the current modulated signals provided via the return channel. FIG. 1 shows a data receiving circuit according to conventional art that may be used to receive current modulated signals via a DiSEqC return channel. In particular, the conventional data receiving circuit of FIG. 1 includes RLC circuitry for converting a pulsed 45 mA current modulated signal provided from an LNB or switching unit to a semi-sinusoidal voltage signal. A depiction of the pulsed current modulated signal and the resultant semi-sinusoidal voltage signal for two different frequencies is shown in FIGS. 2 and 3. In FIG. 1, the resultant semi-sinusoidal voltage signal is sliced by a subsequent data slicer circuit to generate a sliced digital output signal which may then be envelope and edge detected by a processor (not shown in FIG. 1).
With the conventional data receiving circuit of FIG. 1, problems may arise when the current modulated signal provided from the LNB or switching unit exhibits different frequencies. In particular, when the current modulated signal exhibits different frequencies, the semi-sinusoidal voltage signal provided by the RLC circuitry exhibits inconsistent amplitudes which can create processing errors in the aforementioned data slicing, envelope detection and edge detection functions. These amplitude inconsistencies are evident from the waveforms shown in FIGS. 2 and 3. In FIG. 2, for example, waveforms are shown for the current modulated signal provided from the LNB or switching unit at a frequency of 22 kHz (i.e., lower waveform), and the resultant semi-sinusoidal voltage signal provided by the RLC circuitry (i.e., upper waveform).
The waveforms of FIG. 2 may be contrasted with the waveforms of FIG. 3. In FIG. 3, waveforms are shown for the current modulated signal provided from the LNB or switching unit at a frequency of 88 kHz (i.e., lower waveform), and the resultant semi-sinusoidal voltage signal provided by the RLC circuitry (i.e., upper waveform). Comparing the voltage waveforms of FIGS. 2 and 3, it is evident that the amplitude of the semi-sinusoidal voltage signal provided by the RLC circuitry decreases as the frequency of the current modulated signal provided from the LNB or switching unit increases. In this manner, the amplitude of the semi-sinusoidal voltage signal provided by the RLC circuitry of FIG. 1 is dependent upon the frequency of current modulated signal provided from the LNB or switching unit. When the amplitude of the semi-sinusoidal voltage signal provided by the RLC circuitry is below a given threshold, processing errors may occur in the aforementioned data slicing, envelope detection and edge detection functions.
Accordingly, there is a need for a data receiving circuit capable of avoiding the foregoing problems by properly receiving current modulated signals having a wide range of frequencies. The present invention addresses these and/or other issues.